Rebuilding a 2007 RX8. Put it all together, compression was low. Pulled it apart and found that some of the side seals are completely stuck or partially stuck in their groove. It's a "width" clearance problem, not a "length" clearance problem. That is, we have the proper distance between the ends of the side seals and the corner seals. But what seems to be happening is the channel the side seals fit in is too narrow.

The motor did have a broken apex seal (we think) so there may have been that rattling around. The rotor doesn't look damaged, though.

So (aside from buying new rotors, which are really expensive), what's a good way to increase the clearance. And what should the clearance be?

Will sand paper in the groove work?

Any ideas?

Here's a picture to show you what's going on.



Thank you for the help!

 

New rotor time.

 

I really don't want to spend $700 on rotors. Am hoping to sand or file the groove.

 

Well hoping is not how you get things done properly. These are tight tolerances, sand paper and files are not going to fix this. This is why the workshop manual needs to be followed to the T when determining what parts are reusable and what parts are not.

 

9k is completely right. Though, I'm wondering. How did you clean the grooves before putting the new seals in? Seems like most people use an old side seal and scrape it out pretty good. There's going to be some carbon buildup in there.

If you're going to do it yourself, which is highly recommended against. You *CAN NOT* build an engine like this. The tolerances need to be measured, precisely, at a variety of points. There's no way to tell if something "doesn't look good" when the difference between working, and not, is measured in the thousandths of an inch.

 

Yeah I don't understand how these would be installed this way without noticing the issue, but this is exactly why I recommend a professional builder.

 

Part of this project is the fun of building it, though. it did feel a little sticky going in, but not fully stuck, but I guess when squeezed together in the engine, it went in deeper than we tested.

 

I'll bet $9,000 USD that you had the rotor on its edge for a bit while cleaning or some other task. It takes very minimal pressure to bend that metal. You need new rotors, you will need to send the entire rotating assembly off to be balanced as well.

You'd be better off swapping in an SR20 at this point.

 

Are you having fun now? Will it be fun when you try to half *** the rebuild again and then be right back here for the second time?

Do it once, do it right.

 

You can actually kind of see where the clearance closes up around the middle of the side seal. I couldn't really fathom how the grooves lost clearance until you mentioned that though, probably pretty likely.

 

I've seen it first hand even resting on the rotor face bends them out of spec. For storage and cleaning you need to rest them on their side.

 

Judging from the picture you posted above it appears that the rotors were contacting the side housings at some point. Did the motor have a bearing issue before the rebuild? If that's the case replace the rotors, they are ruined and you will want to resurface or replace the side housings because they are usually damaged as well.

 

Yes, the bearings went out on this motor. We replaced the bearings and the crank (which was very scored). The irons have some wear from the incident, but not too much. Rotors have some wear on the sides from it. And I can see what you mean that if the rotors were rubbing the irons that the seal grooves would be impacted like this. But "ruined"?

 

Very fine tolerances.

 

Would you rebuild a piston engine with pistons and bores that had ground into each other?

 

"some wear" is not a spec.

 

true story lmao

Technically you don't need to rebalance if you buy rotors with the same letter designation stamped on the original rotors. A dirty little secret is the original factory balancing was pretty much doo-doo most of the time and anyone wanting a quality rebuild should get the rotating assembly balanced